Currently the bulk of commercial office space is finished using suspended ceiling systems. In such systems rails are assembled into a ceiling grid which is suspended from major structural elements in order to form a framework into which ceiling fixtures are set. The rails making up the grid are flanged to form horizontal frames which support acoustical tiles or other ceiling fixtures. In this manner space is provided for ductwork and power lines between the superposing structural members and the suspended ceiling depending therefrom.
It is neither convenient nor necessary to directly suspend each rail member during grid assembly. Typically, primary or "main tee" rails are directly suspended from the structural members above during construction and secondary rails such as "cross tees" or "sub tees" are then connected to the suspended primary rails. These connections require sufficient strength to support ceiling tiles and other fixtures and preferably provide flush interior flanges to impart stability to the inset fixtures and flush exterior flanges for an aesthetically pleasing appearance.
In addition to requirements of strength and stability, the connection of rails into the grid system must allow for quick connections, ease of assembly, and preferably provide for nondestructive disassembly. The ease of assembly and disassembly is particularly critical in construction practices requiring tedious overhead operations. Prior practices are deficient in meeting these requirements as can be illustrated with a sampling of the prior art.
First consider the cross tee-to-main tee connection system disclosed in U.S. Pat. No. 3,798,865. This grid connection system uses a clip that extends from a substantially perpendicular base plate which is held within a pair of grooves against the web of the main tee. The base plate of this clip rotably inserts into grooves where the plate can be spot welded in place against the web and the grooves crimped on either side to further secure the position of the clip relative to the main tee. The free end of the clip extends outwardly from the base plate and main tee and it is to this extension that the cross tee is fastened. The use of a screw is illustrated in this patent to fasten the cross tee to the clip. The presence of lower flanges severely handicaps the performance of these installation procedures if attempted from any position below the grid; and further, even if this handicap is overcome, this assembly technique proves time consuming, requires relatively skilled labor, and requires a variety of tools for the assembly operation.
U.S. Pat. No. 3,093,221 discloses another main tee-to-cross tee connection system. Here hooks on the clip register into apertures through the web of the cross tee and a detent tab is brought into one of these apertures to prevent unhooking. A spring "nose" on the extended free end of the clip engages an aperture located in the web of the main tee. This arrangement uses two separate and vertically disposed apertures through the web of the main tee when cross tees are connected in coaxial alignment on either side of the main tee. Under this system each clip-to-main tee connection is independent and does not cooperate to increase either the strength or the stability of the joint. Finally, note that this arrangement is limited to main tee-to-cross tee connection as is not readily adaptable to main tee-to-main tee connection.
Compare the cooperation of the clips in U.S. Pat. No. 3,015,375. However, this system requires dissimilar clips which require dissimilar assembly operations. Further, neither of the cross tees is secure until both have been placed. Finally, this arrangement fails to provide for positive engagement and depends upon gravity to maintain the connection.
U.S. Pat. No. 2,990,921 shares this last defect as it has no positive engagement and similarily depends upon gravity to maintain the clip connection. This results in a less rigid and less stable grid.
U.S. Pat. No. 3,321,879 discloses another arrangement for connecting main tees-to-cross tees. This arrangement requires relatively extensive shaping of an end of the cross tees in order to establish a tongue. The tongue configuration allows a clip to be coaxially received onto the cross tee. A portion of the clip engages the base of the tongue to limit further insertion and a detent finger engages an aperture in the tongue to prevent withdrawal. The extended free end of the clip terminates with two detent fingers that engage the distal side of the web of the main tee once the clip is inserted through an aperture in that web. Again, coaxial attachment calls for vertically disposed cross tee-to-main-tee connections. Note the efforts that have been taken to prevent interference of the clips and rails in passing. However, this arrangement makes no attempt to promote stability and strength through interaction of the passing clips.
The systems discussed above are further representative in that none of those systems are readily adaptable to both cross tee-to-main tee and main tee-to-main tee connections. Few clip arrangements are. One current practice that does, however, possess this versitility is the use of clips which must be manipulated to project tabs through slots in each rail. The protruding ends of the tabs are bent down after insertion. Like most of the systems discussed above, this last method of grid assembly requires workmen to perform several operations that are difficult to perform over one's head, particularly where the operation requires reaching around the extended flanges of the rail. The alternative to overhead assembly is to further elevate the workman, beyond that height at which the suspended main tees can first be comfortably reached, to an elevation where the suspended rails are eye level or lower in relation to the average workman. However, this addition to platform elevation creates a significantly more hazardous and difficult working environment and requires increased exertion in each of the many platform relocations required. Further, a platform elevation that allows clip-to-rail connection at eye level or below is then too high for convenient installation of fixtures into that grid.